Stress Analysis of TEE

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Finite Element Analysis of Pipe T-J oint

P.M.Gedkar#1,#Pg Student of Dept of Mechanical Engineering

R.C.E.R.T, Chandrapur, [email protected]

Dr. D.V. Bhope*2* Professor, Dept of Mechanical Engineering

R.C.E.R.T, Chandrapur, [email protected]

Abstract- This paper reports stress analysis of two pressurized cylindrical intersection using finite elementmethod. The different combinations of dimensions of run pipe and the branch pipe are used to investigate thestresses in pipe at the intersection. In this study the stress analysis is accomplished by finite element packageANSYS.

Keywords Stress analysis, Finite element method, Pipe T-joint.

1. Introduction

A pipe is a general term used for hollow product having circular, elliptical or square cross section or forthat matter cross section of any closed perimeter. A pipe is tubular product of cross section that has specificsizes and thicknesses governed by particular dimensional standards. Thus while tubes can be ordered for anyouter diameter (DO), inner diameter (DI) or thickness, pipes have specific sizes and thickness and have to beordered based on these size or thickness.

A piping component experiences two main categories of stresses. The first category of stress comes from

the pressure, either internal or external. The second category of stress comes from the forces and momentsgenerated by weight, thermal expansion, wind, earthquake, and so forth. As the present work deals with thestresses due to internal pressure only, the discussion of stresses due to internal pressure is carried out in thiswork.

Failure is a result of a stress condition which is more severe than the material can withstand. The actualcondition may depart from those assumed at the design stage. Under a steady application of load (e.g. pressure),it ensures against failure of the system as perceived by one of the failure theories. If a pipe designed for a certainpressure experiences a much higher pressure, the pipe would rupture even if such load (pressure) is applied onlyonce. The failure or rupture is sudden and complete. Such a failure is called catastrophic failure.The causes of failures may be due to following

The actual loading may exceed the expected value. Stress concentration at the intersection.

The main cause of pipe T-joint failure is the maximum Von-mises stress induced at the intersection of pipe T-

joint. Hence it is necessary to evaluate the stress at the intersection of pipe T-joint.

2. L iterature Review

Many researchers carried out in pipe T-joint stress analysis. Farid Vakili - Tahami, MohammadZehsaz[1] investigated the thermo-mechanical stresses as well as the temperature distribution along the pipe wallthickness. The results highlight the fact that to evaluate the risk of burn-through, not only the inner walltemperature of the main pipe should be checked against the critical level of 980oC, but also the level of theeffective stresses must be compared against the temperature dependent yield stress of the material. Shiji Guo,Ryoko Morishima[2] investigated stress and buckling analysis and experiment of a composite sandwich T-jointunder shear load were conducted. The result shows that, the traditional T-joint configuration has advantages inboth strength and stiffness at the cost of manufacture complexity. Improved design options for lower cost and

simpler manufacture process were also proposed and analyzed the result. T. Ahmad, M. A. Khan and D.Redekop [3] investigated the quantitative information for the stress concentration and collapse load of

P.M.Gedkar et al. / International Journal of Engineering Science and Technology (IJEST)

ISSN : 0975-5462 Vol. 4 No.01 January 2012 163


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pressurized shell intersections without and with local area wall thinning. Experimental results are not availablefor comparison. In future work it is intended to determine the effect of further mesh modification on thenumerical results, to find results for other types of local area wall thinning, and to determine the fatiguecharacteristics of intersections under cyclical loading.

3. Scope and Methodology

It is evident from the geometry of pipe T-joint that, there is change in geometry at the intersecting junctionwhich leads to stress concentration effect at the intersecting junction. Due to this, probability of failure increasesat this location. It is seen from literatures that, no appropriate finding are available for stresses at intersectingjunction with respect to variation of geometry of run pipe and branch pipe.

In this work an effort is made to study the stresses at intersecting junction by varying the geometricalparameters of run and branch pipe. T pipe joint is considered for stress analysis. The finite element analysis iscarried out by using ANSYS. The loading under only internal pressure is considered. The results of the finiteelement analysis for certain locations are verified with the help of standard analytical relations of pipe.Nomenclature of pipe T-joint is shown in Fig.1.

The finite element analysis of pipe T-joint is performed by considering the following parameter.

Variation in the outer diameter ratio of run pipe and branch pipe.[(DO)b/(DO)r] from 1 to 0.4. Variation in thickness of run pipe and branch pipe.[(DI)b/(DO)b] &[(DI)r/(DO)r] from 1 to 0.4. Variation in the included angle between run pipe & branch pipe () from 300 to 900.

Fig. 1 Nomenclature of Pipe T-Joint

Where,(DI)b =Inner diameter of branch pipe.(DO)b =Outer diameter of branch pipe.(DI)r =Inner diameter of run pipe.(DO)r =Outer diameter of run pipe. =Included angle.

Results obtained by finite element analysis are compared with analytical analysis for location awayfrom intersecting junction.

4. Model of Pipe T-J oint

In this work simple pipe T-joint is used for analysis. The branch pipe is attached with run pipe with anangle of 900. The model is shown in Fig.2, in which ANSYS is used for modeling the pipe T-joint. The modelhas main pipe length of 300mm and branch pipe of 150mm. The advantage of symmetry is taken while analysisby imposing symmetric boundary conditions and the quarter model of pipe T-joint is shown in Fig.3.




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Fig. 2 Pipe T-joint Fig. 3 One Fourth Model of Pipe T-Joint

5. Results

The analysis reveals the stress distribution over the pipe T-joint. The location of maximum stress ispresent at the intersection of pipe. The results are presented in forthcoming sections.

5.1 Stresses in pipe T-J oint with respect to variation in (DO)b/(DO)r and (DI)r/(DO)r

The stress analysis of pipe T-joint with (DO)b/(DO)r =1 revealed the stresses at pipe intersection. Von-mises stresses at the intersection are shown in Table 1. These stress values are evaluated for (DI)b/(DO)b varyingfrom 0.8 to 0.96 and (DI)r/(DO)r varying from 0.8 to 0.96.

Table 1 Maximum Von-Mises Stresses (Mpa) at the Intersection of Pipe

(DI)b/(DO)b (DI)r/(DO)r0.96 0.92 0.88 0.84 0.8

Maximum Von-Mises Stresses (Mpa)0.8 174.87 94.939 86.135 73.978 56.1580.84 101.24 78.033 60.942 50.564 43.158

0.88 76.008 60.933 50.49 42.815 37.3350.92 61.207 50.578 43.655 38.072 34.0010.96 51.714 43.676 37.566 33.666 31.347

The values of the Maximum Von-Mises Stresses at the intersection of the pipe T-joint are plotted inFig.4.

Fig. 4-Variation of Max. Von Mises Stresses at the Intersection of Pipe

The following Fig. 5 and Fig. 6 shows the variation of Max. Von-mises stress in the branch pipe andrun pipe away from the intersection.




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Fig. 5 - Variation of Max. Von-Mises Stresses Fig. 6 - Variation of Max. Von-Mises Stressesaway from Intersection in Branch Pipe away from Intersection in Run Pipe

Figure 7 & 8 shows the comparison between hoop stresses calculated analytically and by FEM awayfrom intersection.

Fig. 7 Comparison between hoop stresses Fig. 8 - Comparison between Hoop stressescalculated analytically and by FEM away from calculated analytically and by FEM away fromintersection in Branch Pipe intersection in Run Pipe

It is seen from the Fig.7, 8 that the hoop stresses away from intersection evaluated analytically and byFEM are quite closer. This verifies the exactness of FE solution.

The stress analysis of pipe T-joint with (DO)b/(DO)r =0.8 revealed the stresses at pipe intersection.These stress values are evaluated for (DI)b/(DO)b varying from 0.75 to 0.95 and (DI)r/(DO)r varying from 0.8 to0.96. The values of the Max. Von-mises stresses at the intersection of the pipe T-joint are plotted in Fig. 9.

Fig. 9 - Variation of Max. Von-Mises Stresses at the Intersection of Pipe




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The stress analysis of pipe T-joint with (DO)b/(DO)r =0.6 revealed the stresses at pipe intersection.These stress values are evaluated for (DI)b/(DO)b varying from 0.667 to 0.93 and (DI)r/(DO)r varying from 0.8 to0.96. The values of the Von-mises stresses at the intersection of the pipe T-joint are plotted in the Fig. 10.

Fig. 10 - Variation of Max. Von-Mises Stresses at the Intersection of Pipe

The stress analysis of pipe T-joint with (DO)b/(DO)r =0.4 revealed the stresses at pipe intersection.These stress values are evaluated for (DI)b/(DO)b varying from 0.5 to 0.9 and (DI)r/(DO)r varying from 0.8 to0.96. The values of the Max. Von-mises stresses at the intersection of the pipe T-joint are plotted in the Fig. 11.

Fig. 11 - Variation of Von-Mises Stresses at the Intersection of Pipe

5.2 Stresses in pipe T-J oint with respect to variation in (DO)b/(DO)r , (DI)r/(DO)r and included angleThe stress analysis of pipe T-joint with (DO)b/(DO)r =1 for included angle=60

0 revealed the stressesat pipe intersection. These stress values are evaluated for (DI)b/(DO)b varying from 0.8 to 0.96 and (DI)r/(DO)rvarying from 0.8 to 0.96. The values of the Max. Von-mises stresses at the intersection of the pipe T-joint areplotted in the Fig. 12.




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Fig. 12 - Variation of Max. Von-Mises Stress with Included Angle 600 at Intersection

The stress analysis of pipe T-joint with (DO)b/(DO)r =1 for included angle=450 revealed the stresses

at pipe intersection. These stress values are evaluated for (DI)b/(DO)b varying from 0.8 to 0.96 and (DI)r/(DO)rvarying from 0.8 to 0.96. The values of the Max. Von-mises stresses at the intersection of the pipe T-joint are

plotted in Fig. 13


The stress analysis of pipe T-joint with (DO)b/(DO)r =1 for included angle=300 revealed the stresses

at pipe intersection. These stress values are evaluated for (DI)b/(DO)b varying from 0.8 to 0.96 and (DI)r/(DO)rvarying from 0.8 to 0.96. The values of the Max. Von-mises stresses at the intersection of the pipe T-joint areplotted in the Fig. 14.





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6. Discussion Conclusion

1. It is observed from the Figs. 4, 9, 10, 11 that as the thickness of branch pipe goes on reducing the stressat the intersecting junction are also reducing, and as thickness of run pipe increases the stresses are alsoreducing at the intersecting junction. It means the behaviour of stress at intersection is exactly reversedfor branch pipe thickness and run pipe thickness. It means that the lower value of branch pipe thicknessare preferable for lower stress values at intersecting junction provided the stresses in branch pipe arewithin the safe limits. This reduction of stresses at the intersection with lesser branch pipe thicknessmay be due to the less constraining effect of branch pipe on the run pipe.

2. From Figs. 4, 9, 10, 11 it is observed that as the thickness of run pipe increases, there is no appropriablechange in Von-mises stress at intersecting junction with respect to change in branch pipe thickness.Thus for thicker run pipe the variation in the thicknesses in branch pipe do not play important role inreduction of Von-mises stresses at intersection.

3. From Table no. 1 and also from the Figs. 4, 9 it is observed that, as the thickness of run pipe & thebranch pipe reduces the stresses in the branch & run pipe away from the intersection point increases.Though it is desirable to have the lesser value of branch pipe thickness for lesser von-mises stress atintersection point but lesser thickness of branch pipe will lead to increase in the stresses in the branchpipe. Thus the thickness of branch pipe plays a dominating role in the stress distribution at intersectionpoint. Thus, judicial choice is necessary to decide the branch pipe thickness.

4. It is seen from the Fig. 4, 9, 10, 11, 12, 13 & 14 that as included angle between the branch pipe and runpipe varies from 900 to 300 , the stress levels goes on increasing. The trend of variation in nature ofstresses is almost identical for all the cases. Thus the 900 included angle give the least stress values thanthat of 300 included angle. This rise in stress with respect to decreasing the angle between run pipe andbranch pipe may be due to increase in stress concentration effect due to oblong opening at the run pipe.

References

[1] Farid Vakili - Tahami, Mohammad Zehsaz. Finite Element Analysis of in welding of T-joint pipe European Journal of ScientificResearch ISSN 1450-216X Vol.40 No.4 (2010), pp.557-568 EuroJournals Publishing, Inc. 2010

[2] Shiji Guo, Ryoko Morishima. Sandwich T-joint structure with & without cutout under shear load. Paper presentation The OhioState University.

[3] T. Ahmad, M. A. Khan and D. Redekop Pressurised Shell Intersections with Local Area Wall Thinning paper presentation SMIRT19, Toronto,Transactions,August 2007.[4] H. Salem, E. A. Soliman, S. A. Ibrahim and K. F. FakhrY Strength of hollow[5] section t-joints under bending moments paper presentation of Ain Shams University Faculty of Engineering Department of Structural

Engineering 2007.[6] Lip.H.Teh, K im J.R. Rasmussen Strength of welded T joint truss connection between equal width cold formed RHS.



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Stress Analysis of TEE